FIG. 5 schematically depicts the structure of a conventional microlithography system employing an electron beam as a lithographic energy beam. A main unit 100 of the system includes an illumination-optical-system (IOS) lens column 101, a reticle chamber 103, a projection-optical-system (POS) lens column 105, and a substrate chamber 107. The IOS lens column 101 is a vacuum chamber that contains an electron gun (serving as the electron-beam source) and the illumination-optical system itself, including beam-shaping aperture, condenser lens(es), beam deflector(s), etc. (not detailed, but well understood in the art). The POS lens column 105 also is a vacuum chamber that is connected downstream of the IOS lens column 101 with the reticle chamber 103 therebetween. The POS lens column 105 contains the projection-optical system, comprising projection lens(es), beam deflector(s), correction coil(s), etc. (not shown, but well-understood in the art). Inside the reticle chamber 103 (also a vacuum chamber) is a reticle stage 104 that supports and positions the reticle for exposure. Inside the substrate chamber 107 (also a vacuum chamber but located downstream of the POS lens column 105) is a substrate stage 108 that supports and positions the substrate (e.g., resist-coated semiconductor wafer) for exposure.
A reticle load-lock chamber 111 is connected to the reticle chamber 103 at the right in the figure. A vacuum-side transport robot 113 is provided inside the reticle load-lock chamber 111 as a reticle-exchange means. An atmosphere-side transport robot 115 and reticle stand 119 are situated at the right of the reticle load-lock chamber 111 in the figure. A reticle cassette 117 is placed on the reticle stand 119. A reticle 120, defining a pattern for use in microlithography, is situated inside the reticle cassette 117.
When exchanging reticles, the reticle 120 inside the reticle cassette 117 is placed manually on the reticle stand 119 by an operator. Upon receiving a reticle-load command from the operator, the atmosphere-side transport robot 115 removes the reticle 120 from the reticle cassette 117 and transports the reticle to inside the reticle load-lock chamber 111. Then, the reticle load-lock chamber 111 is exhausted to a suitable vacuum level by a vacuum pump (not shown, but well-understood in the art). When the required vacuum level is reached inside the reticle load-lock chamber 111, the vacuum-side transport robot 113 transports the reticle 120 from the reticle load-lock chamber 111 to inside the reticle chamber 103 and places the reticle on the reticle stage 104. After the reticle 120 is placed on the reticle stage 104, final reticle positioning and alignment are performed in preparation for exposure.
The conventional device and operational sequence described above are subject to the following problems:
(1) When exchanging reticles, the operator must place the reticle 120 inside the reticle cassette 117 on the reticle stand 119 each time. Hence, whenever microlithographic exposures are being performed using multiple different reticles, this manual operation consumes substantial time and effort.
(2) When transporting a reticle 120 from inside the reticle cassette 117 to inside the reticle load-lock chamber 111, the reticle moves from atmospheric pressure to a reduced-pressure atmosphere. This change is accompanied by a temperature change of the reticle. The reticle also experiences a significant temperature change when being used for exposure. These changes require substantial time for stabilization.